Geoinformation for Disaster and Risk Management - ISPRS

Communication component
Widespread and cost-effective deployment of a GSN
especially needs to make use of commercial off-theshelf
wireless communication techniques and
standardized protocols. An infrastructural WLAN is
used for the connection of the SNs in the field.
Compared with conventional radio data
transmission, the key benefits of a WLAN are: more
cost-effective acquisition; easier addressability of the
SNs; lower power consumption in autarkic usage;
not subject to authorisation requirements; different
possibilities of encryption exist; and a suitable high
data transfer rate is achievable, which is a
precondition for using the LC PDGNSS approach.
All measuring devices are connected to
wireless/wired device servers, which normally
operate with two or more serial ports. Such a unit
serves as a serial port to an Ethernet converter and
comprises an essential interface between every SN
and the communication network. To bridge distances
of more than 500m, special external antennas are
used to provide adequate WLAN connectivity, even
in environmental extremes such as heavy rain, ice
and snow. However, a more or less free line-of-sight
between the transmitters and receptors is essential.
Autarkic power management
Secure energy supply of the SNs is of top priority,
especially for long-term monitoring without loss of
data and permanent year-round operability in
mountainous regions. The concept at Aggenalm
provides solar panels together with back-up
batteries. Additionally fuel cells are an alternative
option. Based on the total power consumption of
about 2.9W for a single LC PDGNSS SN as shown in
Fig. 2b, back-up batteries with a capacity of 130Ah
are chosen to enable the system to operate
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continuously for up to 20 days without need for
recharging. This time span called autonomy factor
seems to be suitable for Alpine environmental
conditions which receive snow for nearly 6 months
in a year and have long periods of overcast sky.
Charge controllers protect the batteries from total
discharge or overcharge and also transmit metadata
to the system administrator predicting potential
failures caused by power shortfalls.
Computing resources
The data sink and processing unit is implemented by
a customary personal computer. Demands for
PDGNSS computing resources at the Aggenalm are
small due to the fact that there are only four SNs onsite.
For a steady program running an uninterrupted
power supply (UPS) is highly recommended. Remote
access and control by a host computer using an
internet connection is an indispensable element of
the developed system, especially because of
maintenance and data backups. Due to missing
infrastructural requirements this is performed by
SkyDSL in the Aggenalm project, see Fig. 1.
Software
Data handling and processing is accomplished
by several different software packages based
on a modular design. The core of the PDGNSS
monitoring component is the Central Control
Application (CCA), see Fig. 3. It is developed
using the graphical programming language
LabView®, National Instruments. All
necessary steps from system initialization,
data collection, to the handover of processed
and checked baselines for subsequent time
series analysis, are actuated and supervised.
Several subprograms, e.g. sensor activation
are termed as virtual instruments (VIs).
The modular, prospective design offers the option to
integrate a great diversity of PDGNSS sensors
(Glabsch et al. 2009b). Interfaces permit embedding
of existing and proven software packages, especially
for baseline processing with e.g. Waypoint GrafNav
(Waypoint 2007). From every embedded software
tool a command line based control is the essential
requirement. Some more details of the CCA are given
in Glabsch et al. (2009a).
Figure 3: Central Control Application (CCA) work
flow (see Glabsch et al. 2009a).